XX1 / X01 setup fun & games: Chain length & strange noise questions

Right, I followed the instructions to the letter but my X01 set up (with XX1 chainring) isn't running right.

It shifts beautifully both ways, finds the 10T cog and doesn't drop or jump (after quite a bit of gaffing with the B-tension bolt). But if I put a lot of pressure through the cranks in 10T cog it sounds as if the chain is rumbling - almost as if I've got the chain wrong on one of the derailleur cogs. It only does it in 10T and none of the others. If I wind the adjuster in or out it makes no difference as far as I can tell.

So could it be chain length? I've used the large-to-large + 4 as instructed but it feels a bit slack and the derailleur is full back in 10T (not touching the cassette but it couldn't cope with much more. Is this normal?

Check it's all running through the mech ok, the jockey wheels are narrow wide too and can jump out of sync.
I find mine quite rumbly under load, either putting power down or if it's muddy, I think this is a lot to do with the narrow wide stuff just being a bit noisier.

My X01 creaked from new, there are issues witht he cassette and mech, all covered under warranty that SRAM are aware of. mainly its the cassette, take it off and grease the hell out of the slined/threaded bit that you screw on. as in a LOT of grease.

Farticus - planning to go 1x10 in the next couple of weeks with a Hope Retainer (narrow/wide) chainring, KMC chain, & Absoute Black cassatte adaptor to 13-40T - is the KMC chain likely to be an issue with the Hope ring? - first I've heard of the issue.